Since semiconductor devices used in various electronic devices, such as a personal computer, and other devices generate heat when driven and the generated heat might build up to adversely affect actuation of the semiconductor devices and peripheral devices, various cooling methods are conventionally adopted. Examples of the cooling methods adopted in electronic elements, such as a semiconductor device, include a method of cooling air in a housing of the device by using a fan attached to the device, and a method of attaching a heat sink, such as a heat dissipation fin and a heat dissipation plate, to the semiconductor device to be cooled.
When a heat sink is attached to the semiconductor device for cooling, a heat conductive sheet is disposed between the semiconductor device and the heat sink to facilitate efficient dissipation of heat from the semiconductor device. As the heat conductive sheet, the one in which fillers, such as scale-like particles of boron nitride (BN), graphite, or the like, and heat conductive fillers of carbon fibers, or the like, are dispersed in a silicone resin. (Refer to Patent Literature 1.)
These heat conductive fillers have anisotropy of heat conduction. For example, when used as the heat conductive fillers, carbon fibers are known to exhibit a heat conductivity of about 600 W/m·K to 1200 W/m·K in a fiber direction, and boron nitride is also known to exhibit a heat conductivity of about 110 W/m·K in a surface direction and a heat conductivity of about 2 W/m·K in a direction perpendicular to the surface direction, thus having the anisotropy.